The present invention relates to an apparatus for heating fuel, especially Diesel fuel and heating oil that is to be supplied to a motor, such as a Diesel engine of a vehicle or stationary unit, or to an oil-burning facility.
A commercially known apparatus for heating Diesel fuel comprises a continuous flow heater that is heated with the battery current of the vehicle and is installed in the fuel line ahead of the fuel filter. When the temperature is low, such a heater prevents precipitation of the paraffin in the fuel, and hence clogging of the fuel filter, by heating the fuel rather than undertaking an otherwise necessary addition of flowability improvers or the like to the Diesel fuel. Such a commercially known electrical Diesel-fuel heater is provided merely in order to heat the Diesel fuel, when frost exists and the temperatures of the Diesel fuel are below 0.degree. C., to only such an extent that precipitation of paraffin can no longer occur in the fuel filter. Due to the enormous amounts of power that such commercial electrical Diesel-fuel heaters require, which represents an additional consumption of energy and places a tremendous load on the vehicle battery, these heretofore known electrical heaters are therefore activated, by a thermally responsive switch, as a function of the fuel temperature, only when the temperature has fallen below freezing; when the temperature is above freezing, the heater is automatically deactivated.
Aside from being faced with the precipitation of paraffin at temperatures below 0.degree. C., Diesel fuel also presents the problem that with Diesel engines, in contrast to internal-reciprocating combustion engines, where the gasoline is to a large extent burned in vaporized form, the Diesel fuel is only atomized by the injection pump in very fine droplets; such fuel droplets are far more difficult to completely burn than is the gasoline air mixture of an internal combustion engine. Complete combustion of the Diesel fuel or oil is possible, if at all, only in the oxygen-rich, i.e. fuel-lean, edge zone of the fuel droplets; the more incomplete the atomization and more incomplete the combustion of the Diesel fuel are, the greater are, in addition to the discharge of nitrogen oxides, above all the generation of smokey and soot-containing exhaust gases and the emission of particulate matter in the Diesel exhaust. A significant improvement of the atomization, and hence a more complete combustion that uses less fuel and reduces the content of pollutants in the exhaust gases, could be achieved if the Diesel fuel were particularly flowable and even less viscous than its normal viscosity at ambient temperature; for this purpose, the Diesel fuel would have to be heated to temperatures in the range of between approximately 40.degree. and 80.degree. C. However, with the heretofore known commercially available electrical Diesel-fuel heaters, this is impossible to achieve because of the enormously high electrical energy that is required.
It is therefore an object of the present invention to provide an apparatus that can be manufactured in an extremely economical manner, that can be installed in a vehicle, even at a later stage, in a simple manner, and with which during cold winter temperatures the Diesel fuel can be heated if necessary in order essentially when the Diesel engine is started to prevent clogging of the Diesel filter due to highly viscous fuel, and at any time of the year, in an economical manner, the Diesel fuel can be continuously heated for operation of the Diesel engine to such an extent that as complete a combustion of the fuel as possible occurs in the Diesel engine, with such combustion additionally using less fuel and producing fewer pollutants.